Power supplies are used in transmitters to supply power to the transmitter. Typical power supplies used in transmitters operate in a closed loop system whereby the voltage is monitored and adjusted based on the output of the transmitter. When the transmitter is keyed tip, a large step in the output current occurs. This large step in the output current results in a large voltage droop of the power supply. Since the power supply is required to provide some minimum voltage to the transmitter during the step of current, if the transient response of the power supply is inadequate, the voltage will droop too low, which causes the transmitter to shut down and the station will not key up.
In a typical power supply control loop, practical limitations force the loop crossover to be much less than what is theoretically possible (typically 1/10-1/4 of the switching frequency). Because of this, large output transients, such as those produced by transmitters, cause the output voltage of the supply to droop until the feedback loop can recover (which may be several seconds).
One solution to improve output transient responses is to provide post regulation on the output of the power supply. The post regulator adds voltage to the output when the transient occurs to reduce the droop. While this approach works fairly well, it requires a substantial amount of circuitry to implement. For example, a second potential source is needed, which may be an additional secondary on the transformer of the supply that is filtered and rectified, and a second control loop. If the second control loop is not properly compensated, the switch-mode loop and the second loop may interfere with each other, causing the power supply to become unstable.
Therefore a need exists for a method to minimize output transient responses in a power supply without the need for a substantial amount of additional circuitry.